The present invention relates to a controlling of a car engine and, more particularly, relates to a method for controlling fuel injection in an engine, in which the delay in the flow of fuel into a cylinder is compensated to keep the quantity of fuel in the cylinder at a requested value with high accuracy.
In car engines, the delay in transport of fuel occurs because of the phenomenon that injected fuel adheres onto walls of an intake manifold or the phenomenon that fuel adhering on walls of an intake manifold is sucked off into a cylinder. Therefore, it is difficult to correctly keep the quantity of fuel in the cylinder at a requested value. To solve this problem, a method as disclosed in Japanese Patent Unexamined Publication No. JP-A-58-8238 has been proposed. According to this proposed method, the quantity of fuel adhering on walls of an intake manifold and the quantity of fuel sucked off into the cylinder from the adhering fuel (hereinafter called "fuel film") are estimated to thereby determine the quantity of fuel supply to keep the quantity of fuel in the cylinder at a requested value.
In an engine of a multi-point fuel injection system in which fuel injection is made considerably before an air-intake stroke (about 90.degree. crank angle before), it can be well considered that all injected fuel stagnates in an intake manifold because fuel injection is terminated before the start of air-intake stroke, in a low or middle revolution speed of the engine. Then, some percent of the stagnant fuel flows into the cylinder in the air-intake stroke. The residual part of the stagnant fuel remains as new stagnant fuel in the intake manifold.
Another method for compensating the delay of the fuel flow by means of a mathematical model of the fuel system has been presented in Japanese Patent Application Laid-open No. 61-126337 and the corresponding U.S. Pat. No 4,939,658 issued on Jul. 3, 1990 and the corresponding European Patent No. 184,626 issued on Jan. 10, 1990.
The conventional technique is constructed on the assumption that some percent of injected fuel always reaches the cylinder. In short, the conventional technique employs a control algorithm in which such flow of fuel is compensated. Therefore, a problem arises in that the delay of fuel caused by stagnancy of all the injected fuel in the intake manifold cannot be compensated.
To keep the quantity of fuel in the cylinder at a requested value, actual fuel injection time must be determined under the consideration of both the phenomenon of adhesion of injected fuel and the phenomenon of sucking off of a part of the fuel film into the cylinder. However, in the conventional technique, actual fuel injection time is determined by subtracting the quantity of sucked-off fuel from the quantity of fuel injection which is determined to keep the quantity of fuel in the cylinder at a requested value under the consideration of only the phenomenon of adhesion of fuel. There arises a problem in that the determination of actual fuel injection time is not rational.
Further, in the multi-point fuel injection system, fuel control must be carried out based on estimation of the quantity of fuel film for each cylinder in order to compensate the transient delay of fuel with high accuracy because the respective cylinders are different from each other in the quantity of fuel film and in the state of the injectors. In the conventional technique, however, the quantity of fuel film only in one cylinder is estimated for all cylinders, and there arises a problem in that the transient delay of fuel cannot be compensated with high accuracy.
Further, in the conventional technique, there is no consideration of the quantity of fuel film for each cylinder. In short, there is no consideration of the difference in the fuel transport characteristic of each cylinder. There arises therefore a problem in that the delay of fuel in some cylinders cannot be compensated with high accuracy in the case where the difference is large.
As described above, a problem in the conventional technique arises in that the quantity of fuel in each cylinder cannot be kept at a requested value though the characteristic of the delay in transport of fuel may be considered.